1. Field of the Invention
The present invention relates generally to a wireless digital communication system for high-speed packet data transmission. More particularly, the present invention relates to a method and apparatus for decoding a concatenated burst in a WiBro system.
2. Description of the Related Art
In the existing Wireless Local Area Network (WLAN), an access terminal (AT), due to its short reach, decreases in performance while on the move or if it goes away from an access point (AP). The wireless Internet based on the third generation mobile communication system, though it does not have the problems of the WLAN, has an increase cost. Wireless Broadband Internet (WiBro), also known as Portable Internet, is the service for allowing a user to enjoy high-speed Internet anyplace and anytime, similar to a mobile phone. WiBro is also an intermediate between the wireless Internet and the WLAN. WiBro uses a frequency band of 2.3 GHz, and has an Internet speed (that is, service bandwidth) of about 1 Mbps.
FIG. 1 illustrates a network configuration of the typical WiBro system.
Referring to FIG. 1, the WiBro system includes a Portable Subscriber Station (PSS) 102 serving as an AT, a Radio Access Station (RAS) 104 serving as an AP, an Access Control Router (ACR) 106 serving as a control station, a Home Agent (HA) 108, and an Authentication, Authorization and Accounting (AAA) server 110. The PSS 102 is an apparatus used by a subscriber to receive portable Internet service. The RAS 104 exchanges data with the PSS 102 via a wireless interface at an end of a wire network, and the ACR 106 controls the PSS 102 and the RAS 104, and routes IP packets. The HA 108 supports IP mobility in the home network, and the AAA server 110 permits access to the portable Internet only for an authorized user, and performs authentication, authorization and accounting on users and devices to provide the portable Internet service. A carrier EP network 112 connects the ACR 106 to the HA 108, the AAA server 110 and a common IP network 114.
The WiBro system uses Time Division Multiplexing (TDM) that divides a downlink and an uplink by time. In the WiBro System, Orthogonal Frequency Division Multiplexing Access (OFDMA) is used as a multiple access scheme. An OFDMA symbol is composed of a plurality of subcarriers. For example, the OFDMA symbol is composed of data subcarriers used for data transmission, pilot subcarriers used for estimation of channel and synchronization, and null subcarriers in which a guard interval and DC subcarriers are included.
Downlink transmission is composed of one preamble symbol, Fundamental Channel (FCH) data and Downlink mapping (DL-MAP) information, and a data symbol, in sequence. The downlink transmission starts from a control symbol, and a guard time used for distinguishing uplink/downlink transmission times is inserted between the downlink and the uplink at the middle and end of an uplink frame.
In the wireless interface, a transmission unit of control information or user data is a concatenated burst with a predetermined size. The concatenated burst is made by concatenating several Protocol Data Units (PDUs) that can be allocated to different users. A Hybrid Automatic Repeat reQuest (HARQ) burst also corresponds to a concatenated burst, as it undergoes a fragmentation process. A FCH burst can also be regarded as a concatenated burst composed of a single block.
A concatenated coding scheme fragments an input burst into fragment blocks using a predetermined concatenation rule, encoding each of the fragment blocks, and concatenating the coded fragment blocks back into a coded concatenated burst. The concatenation process depends on a coding scheme of the burst, the number of subchannels allocated to the burst, a modulation scheme used for the burst, and whether the burst supports HARQ.
The concatenated burst, as described above, includes several PDUs, and each PDU includes therein a 32-bit Cyclic Redundancy Code (CRC) indicating the quality of the corresponding PDU itself. However, concatenated coding of the burst is performed in units of fragment blocks defined in the concatenation rule, rather than in units of PDUs. In each concatenated coding process, because only the fragment blocks are simply encoded, burst quality bits for the entire concatenated burst are not inserted. As a result, in the process of decoding the coded concatenated burst, a receiver cannot obtain burst quality information for the entire concatenated burst. Therefore, the receiver should fully decode the entire concatenated burst, fragment the entire decoded concatenated burst into a plurality of PDUs, and then check a CRC of each PDU in order to determine whether the entire concatenated burst was successfully decoded.
For the HARQ burst or a MAP burst, which is fame control information, an input burst is encoded with a CRC inserted at the tail thereof in order to allow the receiver to measure burst quality information for the entire concatenated burst. Therefore, for the MAP burst and the HARQ burst, the receiver can obtain the burst quality information by checking a CRC included in the decoded burst after completing a decoding process for the entire concatenated burst. In conclusion, the conventional decoding technology cannot obtain the burst quality information for the entire concatenated burst before completing the concatenated decoding on all fragment blocks.
Accordingly, there is a need for an improved method and apparatus for obtaining burst quality information for an entire concatenated burst.